THERMAL MANIFESTATIONS IN NICARAGUA Ariel Zúñiga 1, Melba Su 2 and Mayela Sánchez 2 1 Instituto Nicaragüense de Energía 2 Empresa Nicaragüense de Electricidad (ENEL) INTRODUCTION The north-western shores of the Laguna Blanca in In the Cordillera de los Marrabios, an active this area, shows some weak thermal springs. The temperature Quaternary volcanic range in western Nicaragua (Figure 1), of the water is 36 - 38oC. North of that lake, the Agnuas several geothermal areas have been identified and Calientes springs have temperatures of 38 to 40oC. However, characterized. In addition, field studies and scientific at the bottom of this swampy zone, 60oC have been measured. investigations have shown that significant thermal anomalies Calcium is the main cation, and SO4 and HCO3 are the main and permeable formations exist in the Nicaraguan Depression, anions in these thermal waters. There is some evidence that a large NW-SE trending graben in the central part of the the waters mix with gases ascending from depth. country. Exploration surveys, including drilling, have confirmed the presence of several thermal aquifers at different LAGUNA APOYO depths. Fluids from the Apoyo Caldera are discharging along A number of articles, the latest in the July-August a 4-km long track on the west and south-western banks of the 2003 issue of the Geothermal Resources Council Bulletin, Laguna Apoyo (Figure 2). The sodium-chloride waters have discuss Nicaragua’s high-enthalpy geothermal fields that salinities of about 4000 ppm and temperatures of up to 97oC. produce, or have the potential to produce, fluids appropriate The observed correlation between chloride concentrations and for electricity generation. Here, we describe some of the temperatures, indicate that the fluids are a mixture of hot Na- lower temperature areas. They are associated with surface Cl and cold diluted waters. Geothermometric data suggest that manifestations (i.e., hot springs, mud pots, gas discharges, the hot waters originate at depth at a temperature of at least zone of rock alteration, etc.) so abundant in the Nicaraguan 220oC. Depression. The waters in the Laguna Apoyo are, in fact, equivalent to the thermal waters that surge along the banks of MASAYA-GRANADA-NANDAIME the lake, but they have been cooled and diluted to about half The center of the Masaya-Granada-Nandaime area is their original chloride concentrations. Probably, there is in the southern portion of the Nicaraguan Depression, near the thermal upwelling at the bottom of the lake. city of Diriomo, 45 km southeast of Managua (Figures 1 and 2). It is an active volcanic area that presents important surface TIPITAPA manifestations and includes the Masaya Calera, the Apoyo The Tipitapa area (Figure 3) is on the south-western Caldera (Laguna de Apoyo), and the Mombacho Volcano. shores of Lake Managua (also known as Lake Xolotlán), in Abundant hot springs and furmaroles are found north and the central part of the Nicaraguan Depression. It presents south of the volcano; some are discussed below. several thermal manifestations and some wells have encountered hot waters. A flow of andesitic lavas 12 km LA CALERA southwest of Tipitapa is the closest volcanic feature; the Located north of the Mombacho Valcano, the La Masaya and Apoyo Calderas are 25-30 km to the southwest. o Calera hot springs produces 34 C, Ca-SO4 type waters that Therefore, the origin of these manifestations is thought to be have minor amounts of chlorides. Several dispersed related to the NW-SE trending fractures of the Cofradía furmaroles are also found in this area. The springs flow at a system. rate greater than 1000 L/min. The waters are near saturation At a place called Baños Termales (“thermal baths”) with respect to amorphous silica. Their sulfate content (470 close to the town of Tipitapa, a resort has been constructed. ppm) suggest that the La Calera waters have mixed with It has several hot water swimming pools and a restaurant to condensed steam. The spring waters, however, are not acid. provide recreation as well as benefits from the waters’ They have a pH of 7.6. medicinal properties. The Baños Termales waters have a Na-Cl-SO4-HCO3 RIO MANARES RIVER - MELCATEPE composition and are relatively diluted, with approximately 285 The Rio Manares-Mecatepe area is southeast of the mg/L of alkalinity (as HCO3). The available data suggest that Mombacho Volcano (Figure 2). There are several thermal these 93oC waters are stable in terms of their chemistry and springs in a zone with several swamps and small lakes. The temperature. They do not show evidence of mixing. springs are fed by the Manares River flowing from the northeast. Temperature of the waters varies between 38 and 48oC. GHC BULLETIN, SEPTEMBER 2003 23 VALLE DEL RIO OBRAJE THERMAL SPA “AGUAS CLARAS” The Obraje River valley area (Figure 3), about 10 km The best thermal spa in Nicaragua is at “Aguas northwest of the Momotombo geothermal field, presents Claras.” The facilities are being managed with tourism in numerous thermal manifestations. Several wells show mind. The owners have made improvements so that visitors temperatures of about 40oC. The river, at its headwaters, has can enjoy relaxing in the warm water baths. The spa is located a temperature of around 50oC. It discharges into Lake at kilometer 69 on the Managua-Boaco highway (Figure 3). Managua at an average rate of 90 L/s. In other words, some The Na-SO4 spring waters have a temperature of 6 3 o 2.84 x 10 m of thermal, highly saline, Na-SO4 type water about 50 C and a pH of 8.1. The Aguas Claras spa has six flow into the lake every year. pools with natural thermal waters. A 6-in. diameter pipeline carries the spring’s sulfurous waters directly to the pools by SAN FRANCISCO LIBRE gravity flow. Besides the attraction of the hot pools, there are On the northern banks of Lake Managua, at the San cold water pools, a restaurant, a bar, small ranch houses, as Francisco Libre area (Figure 3), there is a more than 2-km well as air-conditioned rooms. This make the place a required long zone of thermal manifestations (i.e., hot springs, geysers, road stop when traveling between Managua, Boaco and hydrothermal alteration deposits, etc.). The temperatures of Juigalpa. these manifestations varies between 45 and 89oC. Along the shore of the lake, a shallow hot water table exists. It emerges FINAL REMARKS at ground level; where, the rocks are fractured. Several fish Until recently, the development of Nicaragua’s high- kills have been observed near this area. It is quite possible, enthalpy geothermal resources for electricity generation has they were caused by hot fluids discharges from manifestations been the main focus of interest of the government and private at the bottom of the lake. sector. Lately, and because of health aspects associated with To take advantage of the healing properties of the hot hot springs and their economic potential as tourist sites, some waters and muds, a Medicinal Center of Hydro and Mud of the interest has shifted toward the development of a few Therapy has been built at San Francisco Libre with surface manifestation areas. Some investments by government international financial support. The purpose of the center is agencies and private groups have already been made, but to provide treatment to people of limited resources that suffer much could be done considering the country’s abundant low- from illness like arthritis, migraines, rheumatism, muscular temperature geothermal zones. pains, obesity, scabies and allergies (Figure 2). Figure 1. Volcanoes of the Cordillera de los Marrabios. 24 GHC BULLETIN, SEPTEMBER 2003 Figure 2. Details of the Masaya-Granada-Nandaime area. Masaya Masaya Laguna Nicaragua Lake Apoyo Laguna Granada La Calera Mecatepe Nandaime Manares River Figure 3. Location of other thermal areas mentioned in the text. GHC BULLETIN, SEPTEMBER 2003 25.